1. Field of the Invention
The present invention relates to a contact unit and a socket for electrical parts, for electrically connecting two connection objects. In particular, the present invention relates to a contact unit and a socket for electrical parts, for pressing connection objects to be in contact with contacts, which are housed in a hole portion disposed with a conductive member on an internal circumference surface thereof and protrude by being urged outwards by a resilient member, to bend the resilient member, and bringing the contacts into contact with the conductive member at fixed positions, to ensure a stable electrical connection.
2. Description of the Related Art
Heretofore, such a type of contact unit has been disclosed in Japanese Unexamined Patent Publication No. 11-297439, which is applied to a socket for electrical parts used for performance testing of electrical parts. In this contact unit, the main parts of which are shown enlarged in FIG. 14, a plurality of through holes 2 is formed in a guide plate 1 provided on the bottom portion of a frame (not shown in the figure) so as to face contact electrodes 4 of a circuit board 3, conductive films 5 are formed in the internal circumference surfaces of the through holes 2, and the through holes 2 are provided with coil type contacts 6, so as to make contact between connection terminals 8 made of solder balls which are formed in an arrangement on the bottom face of an electrical part 7, and the contact electrodes 4 of the circuit board 3.
In this contact unit, when the coil type contact 6 is pressed from both above and below, by the circuit board 3 and the electrical part 7, respectively, the coil type contact 6 is compressed to be bent, and then, is brought into contact with the conductive film 5 formed on the internal circumference surface of the through hole 2 at points P1, P2 and P3. In this case, short-circuit is caused between P1 and P3 by the conductive film 5, thus the connection resistance between the connection terminal 8 of the electrical part 7 and the contact electrode 4 of the circuit board 3 is reduced, and the inductance is also reduced.
However, in such a conventional contact unit, the bending state of the coil type contact 6 is not limited to that shown in FIG. 14, and sometimes, the coil type contact 6 is bent so as to be in contact with the conductive film 5 at the points P1 and P2 as shown in FIG. 15, for example. In this case, short-circuit is caused between P1 and P2 by the conductive film 5, and the connection resistance is reduced. However, the connection resistance in this case is greater than the connection resistance in FIG. 14.
Furthermore, as shown in FIG. 16, there may be a possibility that the coil type contact 6 is bent so as to be in contact with the conductive film 5 only at the point P2. In this case, since the connection resistance and inductance are those intrinsic to the coil type contact 6, values thereof are greater than those in the cases of FIG. 14 and FIG. 15 as described above.
Thus, according to the conventional contact unit, the bending state of the coil type contact 6 is not constant, and there is a variation in the connection resistance between the plurality of connection terminals 8 of the electrical part 7 and the contact electrodes 4 of the circuit board 3, so that it is not possible to carry out the stable performance testing of the electrical part 7. In particular, this variation in the connection resistance and inductance is caused by unstable electrical connection, so there is a concern that the performance testing of high frequency characteristics of electrical parts would be unreliable.